[firefly] staging: usbip: bugfix for isochronous packets and optimization

Valentina Manea valentina.manea.m at gmail.com
Tue Aug 26 19:06:17 EEST 2014


On Tue, Aug 26, 2014 at 6:12 AM, Dan Carpenter <dan.carpenter at oracle.com> wrote:
> This was promoted out of staging and there wasn't an email to the
> staging list.  Normally I like to go through any remaining questions
> before the code is moved. The code looks pretty good, I just had one
> question.
>

I didn't know I should send to that list as well; will keep in mind
for next time.

>         drivers/usb/usbip/usbip_common.c:712 usbip_pad_iso()
>         warn: why is zero skipped 'i'
>
> drivers/usb/usbip/usbip_common.c
>    687  void usbip_pad_iso(struct usbip_device *ud, struct urb *urb)
>    688  {
>    689          int np = urb->number_of_packets;
>    690          int i;
>    691          int actualoffset = urb->actual_length;
>    692
>    693          if (!usb_pipeisoc(urb->pipe))
>    694                  return;
>    695
>    696          /* if no packets or length of data is 0, then nothing to unpack */
>    697          if (np == 0 || urb->actual_length == 0)
>    698                  return;
>    699
>    700          /*
>    701           * if actual_length is transfer_buffer_length then no padding is
>    702           * present.
>    703           */
>    704          if (urb->actual_length == urb->transfer_buffer_length)
>    705                  return;
>    706
>    707          /*
>    708           * loop over all packets from last to first (to prevent overwritting
>    709           * memory when padding) and move them into the proper place
>    710           */
>    711          for (i = np-1; i > 0; i--) {
>
> I don't understand this loop.  If we really intended to skip the first
> packet then why isn't the "if (np == 0" condition "if (np <= 1"?  That
> would be more clear and the comment would say "if 1 packet then nothing
> to unpack."
>
>    712                  actualoffset -= urb->iso_frame_desc[i].actual_length;
>    713                  memmove(urb->transfer_buffer + urb->iso_frame_desc[i].offset,
>    714                          urb->transfer_buffer + actualoffset,
>    715                          urb->iso_frame_desc[i].actual_length);
>    716          }
>    717  }
>

urb->actual_length is the sum of individual packets' lengths,
urb->iso_frame_desc[i].actual_length. Since actualoffset in the loop
keeps decreasing, it will reach 0 when the first packet is processed.
The first packet's offset is 0 as well and this just does memmove to
the same buffer location.
The (np == 0) condition is *not* the same as (np <= 1) because we want
to return only is there are any packets.
In my opinion, the code is correct as it is. Do you think I should add
an extra comment about the loop?

> Also there is a smatch warning:
> drivers/usb/usbip/stub_tx.c:186 stub_send_ret_submit() warn: returning -1 instead of -ENOMEM is sloppy
>

Noted, will fix after the patch series is upstream.

Thanks,
Valentina


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